Epsametostat

EZH2 has been regarded as an efficient target for diffuse large B-cell lymphoma (DLBCL), but the clinical benefits of EZH2 inhibitors (EZH2i) are limited. To date, only EPZ-6438 has been approved by FDA for the treatment of follicular lymphoma and epithelioid sarcoma. We have discovered a novel EZH1/2 inhibitor HH2853 with a better antitumor effect than EPZ-6438 in preclinical studies. In this study we explored the molecular mechanism underlying the primary resistance to EZH2 inhibitors and sought for combination therapy strategy to overcome it. By analyzing EPZ-6438 and HH2853 response profiling, we found that EZH2 inhibition increased intracellular iron through upregulation of transferrin receptor 1 (TfR-1), ultimately triggered resistance to EZH2i in DLBCL cells. We demonstrated that H3K27ac gain by EZH2i enhanced c-Myc transcription, which contributed to TfR-1 overexpression in insensitive U-2932 and WILL-2 cells. On the other hand, EZH2i impaired the occurrence of ferroptosis by upregulating the heat shock protein family A (Hsp70) member 5 (HSPA5) and stabilizing glutathione peroxidase 4 (GPX4), a ferroptosis suppressor; co-treatment with ferroptosis inducer erastin effectively overrode the resistance of DLBCL to EZH2i in vitro and in vivo. Altogether, this study reveals iron-dependent resistance evoked by EZH2i in DLBCL cells, and suggests that combination with ferroptosis inducer may be a promising therapeutic strategy.

Adult T-cell leukemia/lymphoma (ATL) is a mature T-cell lymphoma with a poor prognosis. Accumulating trimethylation of histone H3 lysine 27 (H3K27me3) caused by upregulated function of either enhancer of zeste homologue 2 (EZH2) or its homolog EZH1 plays an essential role in the maintenance of transcriptional repression in ATL. Selective inhibition of EZH2 may complementarily induce EZH1 activation, so dual targeting EZH1/2 is a rational strategy in developing potent antitumor agents. Valemetostat is the first dual EZH1/2 inhibitor approved for treatment of aggressive ATL in Japan in September 2022. Several other dual EZH1/2 inhibitors such as HH2853, HM97594, and HM97662 have also demonstrated potential in treating malignant tumors. Dual targeting EZH1/2 may have promising antitumor action in hematological malignancies and solid tumors.